SignalBus

Angular signal based message/event bus service for Angular. Under the hood it's using a signal to store and mutate data, the effect() calls the callback function to update subscribers.

Note: Only tested with Angular v18.

Use cases

• Communication between component without a state library, just straightforward communication.
• Widget A updates Widgets B anywhere in the application
• Logger

Playground

Stackblitz

Installation

npm install --save ng-signal-bus

Usage

Basic implementation

import { SignalBusService } from 'ng-signal-bus' 

@Component({
  selector: 'app-widget-add-grocery-items',
  standalone: true,
})
export class WidgetAddGroceryItemsComponent {
  signalBus = inject(SignalBusService)
}

Publish

import { SignalBusService } from 'ng-signal-bus' 

@Component({
  selector: 'app-widget-add-grocery-items',
  standalone: true,
})
export class WidgetAddGroceryItemsComponent {
  signalBus = inject(SignalBusService)

  constructor() {
    this.publish('grocerylist:add', 'Banana')
  }

  publish(key:string, data: any) {
    this.signalBus.publish(key, data)
  }
}

Subscribe

import { SignalBusService } from 'ng-signal-bus' 

@Component({
  selector: 'app-widget-add-grocery-items',
  standalone: true,
})
export class WidgetAddGroceryItemsComponent {
  signalBus = inject(SignalBusService)

  ngOnInit() {
     this.signalBus.subscribe('grocerylist:add', (metaData) => {
      // Outputs { data: 'Banana', timestamp: 1434342 }
      console.log(metaData);
    });
  }
}

Set signal values inside the callback

The callback function runs in the effect() excecution context which not allow to update/write to any signals. To allow this, untracked is used. Untracked will run the function without creating dependencies.

untracked(() => callback(data.metaData));

Example

import { model } from '@angular/core';

items = model<Item[]>([]);

addItem(title: string = '') {
    this.items.update((items: Item[]) => {
      return [...items, { title }];
    });
}

ngOnInit() {
  this.signalBus.subscribe('*', (metaData) => {
    this.addItem(metaData.data);
  });
}